In a drilling operation, steam is required throughout the drilling process and in maintenance operations after drilling has finished. Present systems generally use a conventional boiler housed in a boiler building to generate and supply the steam. Because conventional boilers use an open combustion process, the boiler building must be located at least 26 metres from the wellhead. This presents the disadvantage that the footprint of the lease site must be enlarged accordingly and more tubing is required to bring the steam to the well bore with attendant thermal losses.
Open combustion boilers have a number of additional disadvantages. The open flame is less controlled compared to the use of a flameless system which derives heat from the energy produced by an internal combustion engine. Exhaust gases are often hotter in an open combustion system and if they are not monitored these systems can flood and expel flame. The temperatures in these systems can reach instantaneous temperatures greater than the kindling temperature of natural gas. This means that if there were a natural gas leak, the danger of explosive combustion is present. A diesel or propane leak in the vicinity of the burner can also be ignited.
Further, the combustion process in an open flame system is not as complete as in enclosed systems, which can produce free radicals that escape into the atmosphere. Closed combustion systems have compression ratios commonly many times greater than open combustion burners. This lack of compression negatively affects the reactiveness of oxygen. Hydrocarbon/oxygen reactions are exothermic which provides the heat energy used by the boiler. Provided that the combustion is given enough oxygen, heat and time to complete the process, carbon dioxide and water are produced which are more benign byproducts. However, nitrogen gas is also present during combustion and if the reaction is not ideal, some molecules of nitrogen attach themselves to oxygen to produce the poisonous gas NO. This gas is referred to as a free radical. Other byproducts include carbon monoxide (CO), volatile organic compounds (VOC), and particulate matter (PM). All of these produces are well recognized as being harmful to the environment.
Some open flame systems also require more fuel than a flameless system. Fuel is burned less efficiently in these systems, sometimes requiring a greater amount of fuel to produce an equivalent amount of heat compared to a flameless system.